The long-term objective of this research is to understand the structure (both molecular and organizational) and function (both biological and mechanical) of connective tissues. The specific aims deal with the structure, metabolism and role of proteoglycans in tendon. One aspect of this research addresses the cell biology of tendon that is subjected to compression in specific locations where it wraps around a bone in an animal's joint. At this location a region of tissue develops that has both structural and biochemical similarities to cartilage. In vitro experiments using tendon explants are being carried out to examine the hypothesis that cellular production of large proteoglycans (the kind that imparts compressive stiffness to cartilage) is induced and maintained by a mechanical stimulus. A second aspect of this research addresses the specific interaction of a small proteoglycan with fibrillar collagen. We have determined that the core protein of decorin (a small proteoglycan having only one glycosaminoglycan chain) interacts with high affinity and high specificity with fibrillar collagen type I. The collagen fibrils in all connective tissues appear to have a similar associated proteoglycan. The role of this proteoglycan in tissue function is unknown. It is possible that it plays a vital role in connective tissue function that is interrupted in certain connective tissue disease processes. It is proposed that MBRS students will become involved in experiments to determine the molecular constituents and the biological role of this ubiquitous proteoglycan-collagen interaction.